This application relates to offshore platforms for the exploration for, and production of, undersea petroleum deposits, and, in particular, to the various types of platforms generically known as spars, whether of the classic, truss, or cell spar variety. More specifically, the present invention relates to a spar-type platform, of the type having a buoyant upper hull structure and a lower buoyant section or module that supports the mooring and risers when the upper hull structure is detached, in which the lower section is constructed as a sub-sea mooring buoy (SSMB), wherein the upper hull section is detachably connected to the lower (SSMB) section.
The development of sub-sea petroleum and natural gas deposits in Arctic deep water regions presents special challenges for offshore platform designs. Specifically, platforms in these regions must be able to resist local and global loads from ice in addition to loads conveyed by wind, waves, and currents. In some cases, a platform must be moved to avoid contact with or collision with sea ice and icebergs.
One type of platform that has become widely used for the development of deep water deposits is the spar, especially spars that provide for the storage of petroleum or natural gas. The threat of ice would make it advantageous for the hull of the spar, containing storage or not, to be disconnectable or detachable from its mooring and riser system to avoid impact from the ice. Also, the staged development of a particular deposit may be facilitated by changing out topside facilities (by the detachment of the upper hull structure) as development progresses.